1. Field of the Invention
The present invention relates to a fuel injection controller for controlling fuel injection supply to an engine and a control system used for fuel injection control.
2. Description of Related Art
As is well known, an engine (in particular, internal combustion engine) used as a motive power source of an automobile generates output torque by igniting and combusting fuel, which is supplied through injection performed with injectors, in cylinders. In recent years, automobile diesel engine or the like has come to employ an injection method (a multiple injection method) for performing a sub-injection of an injection quantity smaller than a main injection, which generates output torque, before or after the main injection in one combustion cycle.
Nowadays, fuel combustion noise and increase of NOx emission are regarded as serious problems. As one countermeasure against those problems is to perform a pilot injection or a pre-injection of a small injection quantity before the main injection. In some cases, for example, an after-injection is performed (at injection timing near the main injection) to activate diffusion combustion and eventually to reduce particulate matter emission or a post-injection is performed (at injection timing much later than the main injection) to activate a catalyst through increase of exhaust gas temperature or through supply of a reducing component after the main injection. In recent engine control, the fuel supply to the engine is performed in an injection mode (an injection pattern) that is the most suitable for each of various situations through one or an arbitrary combination of the various injections.
In such the fuel injection control of the multiple injection method, the fuel injection quantity of the sub-injection is much smaller than that of the main injection. Therefore, the pressure in the cylinder (cylinder pressure) as of the fuel injection has a great influence on the injection characteristic. In the case where the fuel injection control of the multiple injection method is employed, it is important to perform the injection control according to the cylinder pressure as of each fuel injection. To this end, for example, as described in Patent document 1 (JP-A-2003-227393), a proposed fuel injection controller variably controls a fuel injection quantity and a fuel injection period according to the cylinder pressure as of the fuel injection. The controller estimates current cylinder pressure by using an adaptation map (i.e., a map beforehand prepared through an experiment or the like) that associates the cylinder pressure at a start of the fuel injection with fuel injection timing (i.e., an injection start angle at the start of the fuel injection). The controller variably controls the fuel injection quantity and the fuel injection period of each fuel injection of the multiple injection on the basis of the estimated cylinder pressure.
The controller can control the fuel injection quantity and the fuel injection period to desired values with higher accuracy because the controller performs the control according to the cylinder pressure as of the fuel injection. However, since the controller senses the cylinder pressure through the estimation using the adaptation map, there is a case where the estimation is difficult depending on the current engine situation and the like. Accordingly, accurate cylinder pressure cannot be necessarily obtained for all of the fuel injections of the multiple injection method.